The former "first lady" of Cambodia's murderous Khmer Rouge regime died Saturday, according to a UN-backed tribunal, without victims ever seeing her face trial on charges of genocide and crimes against humanity.

Ieng Thirith, a French-educated revolutionary who was 83 when she died, was one of the few women in the leadership of the communist movement behind the horrors of the "Killing Fields" era.

She was among just a handful of suspects charged by Cambodia's UN-backed war crimes court, but was freed in 2012 when the case against her was suspended after the court ruled she was unfit to stand trial due to progressive dementia.

Family ties helped her reach the upper echelons of power in a murderous totalitarian regime that tore children from parents and husbands from wives.

The sister-in-law of late Khmer Rouge leader Pol Pot, she served as the regime's social affairs minister alongside her husband, former foreign minister Ieng Sary.

She had been hospitalized this year in Thailand with heart, bladder and lung problems. She passed away in a former Khmer Rouge stronghold on the Thai border where many regime leaders settled after they were ousted by the Vietnamese.

"The accused passed away at approximately 10.30 am (03:30 GMT) on 22 August in Pailin, Cambodia," the UN-backed tribunal said in a statement.

"She was released under a regime of judicial supervision. She remained under judicial supervision until her death," the statement from the Extraordinary Chambers in the Courts of Cambodia (ECCC) added.

"Her body will be cremated on Monday evening," her son Ieng Vuth told AFP by telephone from Pailin, adding his mother had died from cardiac arrest.

Bitter blow

Though the charges against her were never dropped, the suspension of the case against Ieng Thirith was a bitter blow to many who survived the regime, blamed for up to two million deaths.

The Khmer Rouge wiped out nearly a quarter of the population through starvation, forced labour and execution, in a bid to forge an agrarian utopia.

"Now that Ieng Thirith has died, a little part of justice has also died with her," Chum Mey, a survivor of the Khmer Rouge's brutal Tuol Sleng, told AFP.

Her husband Ieng Sary, with whom she had four children, died in 2013 aged 87, before a verdict was delivered in his trial.

Born Khieu Thirith, the daughter of a well-off judge, she recounted earlier that she was initiated into politics by her future husband when they were classmates at high school in Phnom Penh, according to court documents.

She attended university in Paris where she majored in Shakespearean studies and became the first Cambodian to gain a degree in English literature.

The glamour of Paris soon gave way to revolutionary yearnings with Ieng Sary's increasing involvement in radical Marxism.

After returning to Cambodia in 1957 with her husband, she worked as a professor before opening an English school.

By the mid-1960s she was devoting herself entirely to her revolutionary activities with her husband, operating from the Cambodian jungles along the border with Vietnam.

The couple, along with Pol Pot and his wife Khieu Ponnary, would become the ideological center of a nascent communist movement that unleashed unprecedented destruction in the late 1970s.

'Directly involved'

Ieng Thirith was not a member of the regime's powerful standing committee but did sit on its council of ministers, according to court documents.

As social affairs minister, she oversaw the regime's tight control of medicine supplies.

"Ieng Thirith was personally and directly involved in denying Cambodians even the most basic of healthcare during the regime's years in power," said Youk Chhang, director of the Documentation Center of Cambodia which researches the atrocities.

She ordered purges of suspected traitors in her ministry who were sent to re-education camps, and was aware of the regime's killing of perceived enemies, according to court documents.

She allegedly participated in the regime's regulation of marriage -- including its orchestration of mass forced marriages -- and remained a staunch defender of the Khmer Rouge long after its demise in the 1990s.

She was arrested in 2007, along with her husband, and refused to co-operate with the court, consistently denying responsibility for the regime's crimes.

In an outburst in court in 2009 she told her accusers they would be "cursed to the seventh circle of hell".

A small number of top Khmer Rouge leaders have been convicted, including "Brother Number Two" Nuon Chea, 88, and ex-head of state Khieu Samphan, 83.

"Brother Number One" Pol Pot died in 1998 without ever facing justice.